The invention relates to a centrifugal pump impeller.
Impellers for centrifugal pumps can be produced in various ways. In the so-called closed impellers, vanes defining the impeller channels are disposed between two cover plates. These impellers are generally made from castings or sheet material. Casting has the drawback that impellers having narrow outlets cannot be produced by this method because the very narrow casting cores which determine the cross section of the vane channels present difficulties. The British Patent Specification No. 537 727 sets forth a solution for this problem in that a so-called open impeller is produced and converted into a closed impeller by means of a cover plate constituting a separate structural component. For this purpose, a cover plate in the form of a casting having integrally cast vanes is manufactured. This is possible without the use of complicated parts. The small vane height obtained in this manner and the subsequently applied cover plate, which can be riveted or screwed to the vanes at each of a plurality of locations, yield impellers having narrow cross sections.
The German Patent Nos. 509 458 and 737 000 show impellers whose vaneless, suction side cover plates abut vaned, pressure side cover plates and are releasably connected with the impeller hubs. The pumps in question here are for use in the food industry where access to the interior of the impeller, and hence a removable impeller cover plate, are necessary for better cleaning.
From the U.S. Pat. No. 1,849,557, it is known to produce a vaned blank which is just within the limits of casting feasibility. The vanes are exposed in the region of the impeller outlet. By treating the exposed portions of the vanes, e.g., mechanically, the vane width is brought to the hydraulically required dimension and the impeller is thereafter covered using separate cover plates.
The British Patent Specification No. 728 972 illustrates an impeller for centrifugal pumps which is assembled from a plurality of thick-walled components. To prevent damage by cavitation in the inlet region, the flow-directing components are coated with stainless steel or components consisting of stainless steel are used. The suction side cover plate is divided into two parts including a cylindrical inlet ring which forms the suction port and a bent impeller cover plate which is welded thereto in a fluidtight fashion. The vanes themselves, in turn, are welded to the suction side and pressure side cover plates throughout.
Other known solutions such as, for example, that in the U.S. Pat. No. 2,344,444, reside in impellers which are made entirely of sheet material and are assembled from a plurality of individual components. These impellers are predominantly used in the so-called private sector, that is, for applications where low pumping capacities suffice. The use of sheet material impellers for applications requiring large capacities, e.g., standard chemical pumps and the like, creates difficulties in that the impellers do not have the strength to withstand the loads which arise. The consequences are cracks and complete rupture of welds due to overloads, vibrations and the like.